Rubber sheeting with Discover

[John Elliot]

I'm running MapInfo 10.0 and Discover 11.01.

How much distortion should one be able to remove from an aerial photo using the Image Rectify rubber sheeting operation in Discover? 

After rubber sheeting I am still unable to get the aerial photo to perfectly match some points which were collected in the field using GPS with differential correction.

Any comments would be welcome.

 

John Elliot

 

[AlexZ]

Hello John,

Discover's Image Rectification tool can correct/rubber-sheet imagery that has been stretched, skewed or rotated, using a range of transformation methods. However, aerial photography has significantly more distortion than just these issues, and to be viewed correctly and accurately, really needs to be ortho-rectified, allowing for correction of:

- terrain variations (mountain tops closer to the camera will be much less distorted than valley floors), requiring ortho-rectification against a high-resolution DEM. The more undulating the terrain, the more apparent this issue will be.
- tilt of the camera (the corner regions and edges of your airphoto will show much greater distortion than the region directly underneath the sensor)
- flight height of the camera


This sort of work is the provenance of a dedicated image processing/orthorectification package, or something a contractor supplying such imagery should be able to provide as part of that service.

Hope that helps.

Alex Zdziarski
Product Manager
PBS

[John Elliot]

Hello Alex,

Thanks for your reply - what I expected but I was hoping for something else!

I have got a reasonable amount of scale distortion removed but about 10m horizontal variation remains towards the margins of the photo.  Unfortunately orthorectifiction is not available for State aerial photos of the Broken Hill district where I am working so I'll just have to accept what I have.

 

Regards,
John

 

John Elliot
Anzeco Pty. Limited
mineral exploration consulting services
26 Casey Circuit,
Bathurst, NSW 2795, AUSTRALIA
 http://tinyurl.com/ElliotBay
phone: +61 2 6331 4925

 

 

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